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Compressor auto shut off or no?

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ImpactX

ImpactX

Member
May 4, 2019
636
19
Minnesota, United States
I keep hearing folks say, do not shut off your compressor while it's running. Cause the pressure will put stress on the piston and crankshaft. Even compressor with automatic shut off. They say it's not good to let it auto shut off. The right way is to bleed the valve first, then shut off the compressor then quickly closed the tank valve. Does shutting off the compressor with 4500 psi in the line put stress on the compressor or not? Then why would manufacturers put an auto shut off for?
 
I would imagine allowing the compressor to come to a hard stop against 4500psi, I only fill to 4300, is hard on the unit and I know firsthand that rupture discs blow fairly often if one does not release the pressure before shutdown at higher pressures. Auto shutoff is just one more safety feature. If you are distracted and fail to shut the compressor off before pressure damages something it will shut off automatically at the pressure you set it for. This is a big plus for me. I can set it for a bit over 2000pis when I am filling my Discovery, just over 3000psi when filling my 13ci aluminum tanks, 3600psi when filling my Impact, or around 4300psi when filling the smallish 4500psi tanks and feel fairly confident that I am not going to cause damage if I space out on something. This is the reason I purchased the Set Pressure model of the Yong Heng compressor.
 
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That doesn’t sound very logical. I always shut my booster off and crank it up again. Never had a problem. Bleed valve when tank is full & have turned off everything and closed tank.
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I assume that you are referring to the Altaros booster. There is no problem stopping and restarting them under load. In the case of an electric motor-driven compressor, they must be depressurised before attempting to restart. As for depressurizing before shutting down, I know when I let my YH pump auto shut off it blows the pressure release valve on the first stage separator. It does say in the cryptic instructions to release the pressure before switching off saying something about backlash. I can't see why but I do it anyway. I have disconnected the auto-stop so it only stops now when I decide when. 
 
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I have not heard "folks say, do not shut off your compressor while it's running". I can only speak about my AV 4500psi compressor, which is working very well. 

According to the instructions they advise to set a "shut off" pressure, then let the compressor turn off by itself at that pressure. Then flip the compressor on/off switch to off, close your tanks valve (if filling a tank) then bleed the air off, and wait for the unit to cool before turning off the water pump.

What they don't want you to do is turn it off (for some reason) then just start it back up with pressure in the line. Or start it up with you partially filled tank open with that pressure working against the startup of the compressor.
 
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My Yong Heng has auto shut off and I always use it because I hate waiting, even for a couple of minutes. I can't see how shutting off the compressor without bleeding the line can do any damage to the piston, crankshaft or any other parts of the machine. The piston and crankshaft are constantly subject to the working stress caused by two opposing forces: (1) the pressure of the compressed air in the system and (2) the force produced by the motor. When the compressor is shut down with the line still holding air, component (1) will stay but (2) will disappear so the resulting stress can only be lower.

Of course if you bleed the line before shutting off, both components will disappear and the resulting stress will be zero. The question is, what's the point of having zero stress in the last fraction of a second when the compressor has aleady run for minutes under the working stress.
 
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In years past I did maintenance on industrial 4 stage compressors. If a compressor is designed with longevity in mind.

Start up should be with no air pressure on the compressor, this will let the compressor start freely. If there is pressure on the compressor the motor has to start under a load creating higher amperage. if there is enough pressure the motor will be in a locked rotor state. If the motor is protected by overloads they will open and save the motor. If there are no overloads and your supply breaker is Big enough you will burn up your motor. What can be done to prevent this is a unloader valve will be plumed in series with load air line. The exit line is shut off with a valve or one way valve and the unloader opens unloading any pressure on compressor / motor. then the motor shuts down. Now the motor is ready for the next start in a free state. that's a simplified version. If the design is considering water removal and or drying it would have more in the circuit.

All of this can be done with manual valves but should be done in that order.






 
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My Yong Heng has auto shut off and I always use it because I hate waiting, even for a couple of minutes. I can't see how shutting off the compressor without bleeding the line can do any damage to the piston, crankshaft or any other parts of the machine. The piston and crankshaft are constantly subject to the working stress caused by two opposing forces: (1) the pressure of the compressed air in the system and (2) the force produced by the motor. When the compressor is shut down with the line still holding air, component (1) will stay but (2) will disappear so the resulting stress can only be lower.

Of course if you bleed the line before shutting off, both components will disappear and the resulting stress will be zero. The question is, what's the point of having zero stress in the last fraction of a second when the compressor has aleady run for minutes under the working stress.
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This seems logical.
 
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Once I get close to the pressure I want to fill to I shut the valve to the tank and without hesitation crack the bleed valve and slowly unload the compressor before shutting it off even though the AV has a auto-shut down. I used to use the auto-shut off but after a few repairs which are probably not be related I do all I can now to ease the load during these critical moments. Hopefully it'll lengthen the times between repairs.

Jking
 
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My Yong Heng has auto shut off and I always use it because I hate waiting, even for a couple of minutes. I can't see how shutting off the compressor without bleeding the line can do any damage to the piston, crankshaft or any other parts of the machine. The piston and crankshaft are constantly subject to the working stress caused by two opposing forces: (1) the pressure of the compressed air in the system and (2) the force produced by the motor. When the compressor is shut down with the line still holding air, component (1) will stay but (2) will disappear so the resulting stress can only be lower.

Of course if you bleed the line before shutting off, both components will disappear and the resulting stress will be zero. The question is, what's the point of having zero stress in the last fraction of a second when the compressor has aleady run for minutes under the working stress.
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I agree with Airgunfans 100%. It's a myth that it is beneficial to manually release pressure to prevent damage to a compressor under full load instead of allowing an auto shutoff to turn it off. What is important is to not start or restart with air pressure in the compressor which bogs down the motor from back pressure.
 
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